The care of adults with congenital heart malformations has evolved into a specialty in its own right. The malformations are conceived by the general cardiologist as extremely complex, requiring a sound knowledge of embryologic development for their appreciation. The defects are so varied, and can occur in so many different combinations, that to base their descriptions on embryologic origins is at best speculative and at worst utterly confusing. Fortunately, in recent decades great strides have been made in enabling these malformations to be more readily recognizable to all practitioners who care for the patient born with a malformed heart. Undoubtedly, the introduction of the system known as “sequential segmental analysis,” hand in hand with developments in angiography and cross-sectional echocardiography, has revolutionized diagnosis. The key feature of this approach is akin to the computer buff’s WYSIWYG (what you see is what you get), except that in this case it is WYSIWYD (what you see is what you describe). Best of all, it does not require knowledge of the secrets of cardiac embryogenesis.
Cardiac morphology applied to the adult patient with congenital heart disease (CHD) is often not simply a larger version of that in children. Cardiac structures grow and evolve with the patient. Structural changes occur after surgical palliation and correction. Even without intervention in infancy, progression into adulthood can bring with it changes in ventricular mass, calcification or dysplasia of valves, fibrosis of the conduction tissues, and so on. It is, nevertheless, fundamental to diagnose the native defect. The focus of this chapter is on sequential segmental analysis and its terminology.
Sequential Segmental Analysis: General Philosophy
To be able to diagnose the simplest communication between the atria or the most complex of malformations, the sequential segmental approach (also known as the European approach due to the promoters of the original concepts) as described here requires that normality be proven rather than assumed. Thus the patient with an isolated atrial septal defect in the setting of a normally constructed heart undergoes the same rigorous analysis as the patient with congenitally corrected transposition associated with multiple intracardiac defects.
Any heart can be considered in three segments: the atrial chambers, the ventricular mass, and the great arteries ( Fig. 3.1 ). By examining the arrangement of the component parts of the heart and their interconnections, each case is described in a sequential manner. There are limited possibilities for the arrangement of the individual chambers or arteries that make up the three segments. Equally, there are limited ways in which the chambers and arteries can be related to one another. The approach begins by examining the position of the atrial chambers. Thereafter, the atrioventricular (AV) junction and the ventriculoarterial junctions are analyzed in terms of connections and relations. Once the segmental anatomy of any heart has been determined, it can then be examined for associated malformations; these need to be listed in full. The examination is completed by describing the cardiac position and relationship to other thoracic structures. The segmental combinations provide the framework for building the complete picture because in most cases the associated lesions produce the hemodynamic derangement.
The philosophy of segmental analysis is founded on the morphologic method ( Box 3.1 ). Thus chambers are recognized according to their morphology rather than their position. In the normally structured heart, the right-sided atrium is the systemic venous atrium, but this is not always the case in the malformed heart. Indeed, the very essence of some cardiac malformations is that the chambers are not in their anticipated locations. It is also a fact of normal cardiac anatomy that the right-sided heart chambers are not precisely right sided; nor are the left chambers completely left sided ( Fig. 3.2 ). Each chamber has intrinsic features that allow it to be described as “morphologically right” or “morphologically left,” irrespective of location or distortion by the malformation. Features selected as criteria are those parts that are most universally present even when the hearts are malformed. In this regard, venous connections, for example, are not chosen as arbiters of rightness or leftness of atrial morphology. The atrial appendages are more reliable for identification. In practice, not all criteria for all the chambers can be identified in the living patient with a malformed heart. In some cases there may be only one characteristic feature for a chamber, and in a few cases rightness or leftness can be determined only by inference. Nevertheless, once the identities of the chambers are known, the connections of the segments can be established. Although spatial relationships—or relations—between adjacent chambers are relevant, they are secondary to the diagnosis of abnormal chamber connections. After all, the connections, like plumbing, determine the flow through the heart, although patterns of flow are then modified by associated malformations and hemodynamic conditions. The caveat remains that valvular morphology in rare cases (eg, an imperforate valve) allows for description of the connection between chambers, although not in terms of flow until the imperforate valve is rendered patent surgically or by other means.
Determine arrangement of the atrial chambers (situs)
Determine ventricular morphology and topology
Analyze atrioventricular (AV) junctions
Type of AV connection
Morphology of AV valve
Determine morphology of great arteries
Analyze ventriculoarterial junctions
Type of ventriculoarterial connection
Morphology of arterial valves
Infundibular morphology
Arterial relationships
Catalog-associated malformations
Determine cardiac position
Position of heart within the chest
Orientation of cardiac apex
Morphology of the Cardiac Chambers
Atrial Chambers
All hearts possess two atrial chambers, although they are sometimes combined into a common chamber because of complete or virtual absence of the atrial septum. Most often, each atrial chamber has an appendage, a venous component, a vestibule, and a shared atrial septum. Because the last three components can be markedly abnormal or lacking, they cannot be used as arbiters of morphologic rightness or leftness. There remains the appendage that distinguishes the morphologically right from the morphologically left atrium. Externally, the right appendage is characteristically triangular with a broad base, whereas the left appendage is small and hook shaped with crenellations (see Figs. 3.2 and 3.3 ). It has been argued that shape and size are the consequence of hemodynamics and are unreliable as criteria.
Internally, however, the distinguishing features are clear. The terminal crest is a muscular band that separates the pectinate portion—the right appendage—from the rest of the atrium. The sinus node is located in this structure at the superior cavoatrial junction. Because the appendage is so large in the morphologically right atrium, the array of pectinate muscles occupies the entire parietal wall and extends to the inferior wall toward the orifice of the coronary sinus (see Fig. 3.3 ). In contrast, the entrance (os) to the left appendage is narrow, the terminal crest is absent, and the pectinate muscles are limited. The smoother-walled morphologically left atrium, however, has on its epicardial aspect a prominent venous channel, the coronary sinus, which can aid in its identification (see Figs. 3.2 and 3.3 ). Where the septum is well developed, the muscular rim around the oval fossa is indicative of the morphologically right atrium, because the flap valve is on the left atrial side.
Ventricles
Ventricular morphology is a little more complex than atrial morphology in that some malformations may have only one ventricular chamber or one large ventricle associated with a tiny ventricle. Normal ventricles are considered as having three component parts (“tripartite”; see Chapter 46 ): inlet, outlet, and trabecular portions. There are no discrete boundaries between the parts, but each component is relatively distinct ( Fig. 3.4 ). The inlet portion contains the inlet (or AV) valve and its tension apparatus. Thus it extends from the AV junction to the papillary muscles. The trabecular part extends beyond the papillary muscles to the ventricular apex. Although the trabeculations are mainly in the apical portion, the inlet part is not completely devoid of trabeculations. The outlet part leading toward the great arteries is in the cephalad portion. It is usually a smooth muscular structure, termed the infundibulum, in the morphologically right ventricle. In contrast, the outlet part of the morphologically left ventricle is partly fibrous, owing to the area of aortic-mitral fibrous continuity. The mitral valve is always found in the morphologically left ventricle, and the tricuspid valve is always in the morphologically right ventricle, although these features have no value when the ventricle has no inlet. Similarly, the outlets are not the most reliable markers.
Of the three ventricular components, the distinguishing marker is the apical trabecular portion. Whenever there are two ventricular chambers, they are nearly always of complementary morphology, one being morphologically right and the other morphologically left. Only one case has been reported of two chambers of right ventricular morphology. Characteristically, the trabeculations are coarse in the morphologically right ventricle and form a fine crisscross pattern in the morphologically left ventricle. Thus, no matter how small or rudimentary, if one or more component parts are lacking, the morphology of a ventricle can be identified.
In addition to right and left morphology, there is a third ventricular morphology. This is the rare variety in which the trabeculations are coarser than the right morphology and is described as a solitary and indeterminate ventricle ( Fig. 3.5 ). There is no other chamber in the ventricular mass. More often, the situation is one of a large ventricle associated with a much smaller ventricle that lacks its inlet component (see Fig. 3.5 ). Because its inlet is missing, the smaller ventricle is described as rudimentary, but it may also lack its outlet component. The third component—the apical portion—is always present. It may be so small that identification is impossible, but its morphology can be inferred after identifying the larger ventricle. The rudimentary ventricles are usually smaller than constituted ventricles, but not always. Normal ventricles can be hypoplastic; a classic example is the right ventricle in pulmonary atresia with intact ventricular septum (see Fig. 3.5 ) (see Chapter 46 ). Size, undoubtedly important in clinical management, is independent of the number of components a ventricle has.
In clinical investigations, the nature of trabeculations may not be readily identifiable. For instance, the fine trabeculations in the hypertrophied morphologically left ventricle can appear thick. Adjuncts for diagnosis must be considered. In this respect, a review of normal ventricular morphology is helpful. The inlet component of the right ventricle is very different from that of the left ventricle. The tricuspid valve has an extensive septal leaflet together with an anterosuperior and a mural (inferior) leaflet. Tethering of the septal leaflet to the septum is a hallmark of the tricuspid valve. At the AV level, its attachment—or hinge point—is more apically positioned than the point at which the mitral valve abuts the septum (see Fig. 3.3D ). This is an important diagnostic feature, recognizable in the four-chamber section. In contrast, the mitral valve has no tendinous cords tethering it to the septum. The normal, deeply wedged position of the aortic valve between the mitral and tricuspid valves allows direct fibrous continuity between the two left heart valves (see Fig. 3.4 ). Consequently, the left ventricular outlet lies between the ventricular septum and the anterior (aortic) leaflet of the mitral valve. This passage is detected in cross-sectional views as a cleavage or recess between the septum and the mitral valve. Both the anterior (aortic) and posterior (mural) leaflets of the mitral valve are attached to the two groups of papillary muscles situated in anterolateral and posteromedial positions within the ventricles. More accurately, the respective papillary muscles are superiorly and inferomedially situated, as depicted on tomographic imaging.
The normal outlets also have distinctive morphologies. As described earlier, the right ventricular outlet is completely muscular. The conical muscular infundibulum raises the pulmonary valve to occupy the highest position of all the cardiac valves. The infundibulum is not discrete because it is a continuation of the ventricular wall. In its posterior and medial parts, it continues into the supraventricular crest formed in part by the ventriculoinfundibular fold (see Fig. 3.4 ). The crest distances the tricuspid valve from the pulmonary valve. The outlet septum is diminutive or lacking in the normal heart but comes into prominence in hearts with malformed outlets, exemplified by hearts with tetralogy of Fallot or a double-outlet right ventricle (see Chapter 43 , Chapter 50 ). On the septal aspect, the ventriculoinfundibular fold is clasped between the limbs of another muscular structure characteristic of the right ventricle. This is the septomarginal trabeculation, which is like a Y -shaped strap (see Fig. 3.4 ). The fusion of its limbs to the fold of musculature forms the supraventricular crest. Further muscular bundles—the septoparietal trabeculations—cross from the crest to the free (parietal) ventricular wall in the outlet portion. The medial papillary muscle of the tricuspid valve inserts into the posterior limb of the septomarginal trabeculation. The body of this trabeculation extends into the trabecular component, where it gives rise to a characteristic bundle—the moderator band—that passes across the cavity of the right ventricle to reach the free (parietal) wall. This is no longer the outlet region, but its features are useful diagnostic clues for recognizing a right ventricle. In contrast, the left ventricular outlet is smooth (see Fig. 3.4 ); there is no equivalent of the supraventricular crest nor the moderator band.
Great Arteries
The great arteries are recognized by their branching patterns rather than the arterial valves, because the semilunar leaflets are indistinguishable. The coronary arteries arise from the aortic sinuses. As the aorta ascends in a cephalad direction, it arches to the left and gives rise to the neck and arm arteries before turning inferiorly to become the descending thoracic aorta. In adults, the pulmonary trunk is recognized as the great artery that bifurcates into the right and left pulmonary arteries. A third vessel, the arterial duct, may be visualized in infancy. In the normal heart the pulmonary trunk passes anterior and to the left of the aortic root. The aorta and pulmonary trunk ascend in spiral relationships with the aorta arching over the right pulmonary artery (see Fig. 3.2 ).
When there are two great arteries, it is an easy matter to distinguish the aorta from the pulmonary trunk. The aortic sinuses give origin to the coronary arteries in the vast majority of cases. At the arch, the aorta gives branches to the head, neck, and arm. Although some of its branches may be absent in malformations, or its arch may be interrupted, the aorta is the vessel that gives origin to at least one of the coronary arteries and the greater part of the systemic supply to the upper body. The pulmonary trunk rarely gives origin to the coronary artery. It usually bifurcates into the left and right pulmonary arteries ( Fig. 3.6 ). When only one great artery is found, it is frequently presumed to be a common arterial trunk (truncus arteriosus) ( Chapter 37 ). However, care must be taken in making this diagnosis to avoid missing an atretic aorta or atretic pulmonary trunk (see later). A common arterial trunk is defined as one that leaves the ventricular mass via a common arterial valve and supplies the coronary, systemic, and pulmonary arteries directly (see Chapter 37 ). This must be distinguished from the situation often referred to as “truncus” type IV, in which the solitary trunk does not give rise to any intrapericardial pulmonary arteries (a severe form of tetralogy with pulmonary atresia; see Chapter 44 ) (see Fig. 3.6 ). Collateral arteries that usually arise from the descending aorta supply the lungs. A case may be made for such an arterial trunk to be either an aorta or a truncus. For simplicity, this is described as a solitary arterial trunk.
